The present invention relates to compositions containing polycyclic olefins which polymerize under free-radical conditions to generate crosslinked polymers and copolymers. The invention relates particularly to polycyclic olefins which primarily contain bicycloheptenyl unsaturation units.
Polymers and copolymers synthesized from polycyclic olefin monomers have attracted much interest from the scientific community due to the desirable properties often exhibited by these materials. Cyclic olefin copolymers (COC""s) possess a unique combination of properties such as low density, low moisture absorption, low birefringence, high transparency, and high strength. Depending on the polycyclic olefin monomer and the polymerization conditions, materials can also be produced having a wide range of glass transition temperatures. As a result, these materials are being tested for use in diverse applications such as electronics, CD-ROM disks, optical lenses, barrier films, and medical appliances.
A particularly attractive characteristic displayed by polycyclic olefin monomers is the ability to polymerize via a variety of reaction mechanisms. It is well-known that polycyclic olefins can be polymerized and/or copolymerized free-radically, cationically, or coordinatively using organometallic catalysts. Due to this mechanistic flexibility, a wide variety of functionalized comonomers can be incorporated into the cyclic olefin copolymer, which provides further control over the bulk properties of the material.
Since polycyclic olefin monomers have the ability to polymerize free-radically, these monomers have been explored as potential candidates for use in free-radical cured thermosetting compositions. Indeed, polycyclic olefins have been shown to readily copolymerize with electron deficient olefins. Thermosetting resins incorporating polycyclic olefins can be expected to have many desirable properties, such as high Tg, hydrophobicity, and low shrinkage upon cure. However, in order to obtain these desirable properties in a thermoset resin, the polycyclic olefin must be of a certain minimum molecular weight (i.e., the volatility of the olefin should be low) and must be sufficiently reactive with the propagating free radicals during cure to produce a highly crosslinked thermoset network.
Unfortunately, most common and inexpensive polycyclic olefin monomers, such as norbornene, norbornadiene, dicyclopentadiene (DCPD), and the like, are deficient in these areas. Specifically, norbornene, norbornadiene, and DCPD are too volatile for use in many thermoset applications. In addition, the cyclopentenyl unsaturation of DCPD is insufficiently reactive for many thermoset applications. Indeed, it is well known that the cyclopentenyl double bond is far less reactive than the norbornenyl double bond, due to the low ring strain associated with the cyclopentenyl ring (relative to the bicycloheptenyl group). Moreover, the allylic hydrogen atoms on the cyclopentenyl rings may contribute to chain transfer reactions, thereby reducing the molecular weight of the growing polymer chains during cure. Thus, optimum free-radically cured thermosets incorporating polycyclic olefins are only produced when the polycyclic olefin has low volatilty and contains little, if any, cyclopentenyl unsaturation.
Accordingly, there is a need for polycyclic olefin monomers which can be readily incorporated into free-radically cured thermosetting resin compositions, thereby producing thermosets having a unique combination of beneficial properties.
In accordance with the present invention, there are provided free-radically polymerizable compositions comprising polycyclic olefins, wherein the polycyclic olefins contain little, if any, cyclopentenyl unsaturation. As a result, these olefins are sufficiently reactive with the propagating free-radicals during cure to provide a highly crosslinked thermoset resin. Moreover, invention compositions comprise high molecular weight polycyclic olefins having low volatility. Accordingly, the undesirable weight loss upon cure observed with many thermosetting compositions is considerably reduced.
Further provided by the present invention are compositions comprising functionalized polycyclic olefin monomers. These functionalized olefin monomers provide additional benefits such as increased adhesion to a variety of surfaces as well as greater control over glass transition temperatures.
In accordance with the present invention, there are provided free-radically polymerizable compositions comprising
(A) at least one polycyclic olefin monomer, said monomer having at least one terminal norbornenyl functional group, wherein said monomer contains little, if any, cyclopentenyl unsaturation,
(B) a maleimide or succinimide,
(C) optionally, one or more free radical curing co-monomers, and
(D) in the range of 0.2 up to 5 wt % of at least one curing catalyst, based on the total weight of the composition.
In one embodiment, polycyclic olefin monomers contemplated for use in the practice of the present invention have the following structures: 
wherein each R is
(a) independently hydrogen or substituted or unsubstituted alkyl, and each x is independently 0, 1 or 2, or
(b) xe2x80x94Xxe2x80x94Y,
xe2x80x83wherein:
X is an optional bridging group
Y is a maleimide, a substituted maleimide, an epoxy group, an oxazoline, a cyanate ester-substituted aryl, or an oxazine, and
nxe2x89xa6about 8.
In preferred embodiments, X is an alkylene or oxyalkylene comprising up to about 20 atoms, or X is a siloxane, and Y is an optionally substituted maleimide or oxazine. In a particularly preferred embodiment, Y is a benzoxazine.
In another embodiment, polycyclic olefin monomers contemplated for use in the practice of the present invention have the following structure: 
wherein:
R, x, and n are as defined above, and
Q is a bridging group selected from siloxane, 
wherein Rxe2x80x2 is an alkylene, an arylene or a polycyclic hydrocarbyl. In preferred embodiments, Q is a tetramethyldisiloxane.
Maleimides contemplated for use in the practice of the present invention as component (B) have the following structure: 
wherein:
R is hydrogen or lower alkyl
Jxe2x80x94 is:
(1) saturated straight chain alkyl or branched chain alkyl, optionally containing optionally substituted aryl moieties as substituents on said alkyl chain or as part of the backbone of said alkyl chain, and wherein said alkyl chains have up to about 20 carbon atoms,
(2) aromatic groups having the structure: 
xe2x80x83wherein:
each Ar is a monosubstituted, disubstituted or trisubstituted aromatic or heteroaromatic ring having in the range of 3 up to 10 carbon atoms, and Z is:
(i) saturated straight chain alkylene or branched chain alkylene, optionally containing saturated cyclic moieties as substituents on said alkylene chain or as part of the backbone of the alkylene chain, or
(ii) polyalkylene oxides having the structure:
xe2x80x94[(CR2)rxe2x80x94Oxe2x80x94]qxe2x80x94(CR2)sxe2x80x94
wherein each R is independently as defined above, r falls in the range of 1 up to 10, s falls in the range of 1 up to 10, and q falls in the range of 1 up to 50,
(3) di- or tri-substituted aromatic moieties having the structure: 
wherein each R is independently as defined above, t falls in the range of 2 up to 10, u falls in the range of 2 up to 10, and Ar is as defined above,
(4) polyalkylene oxides having the structure:
[(CR2)rxe2x80x94Oxe2x80x94]qxe2x80x94(CR2)sxe2x80x94
wherein each R is independently as defined above, and wherein each of r, s and q are as defined above,
(5) a polycyclic olefinyl, or
(6) mixtures of any two or more thereof, and
m is 1, 2, or 3.
In preferred embodiments, the maleimide is N-methylmaleimide, N-ethymaleimide, N-propylmaleimide, N-butylmaleimide, N-t-butylmaleimide, N-hexylmaeimide, N-2-ethylhexylmaleimide, N-cyclohexylmaleimide, N-octylmaleimide, N-decylmaleimide, N-dodecylmaleimide, N-phenylmaleimide, 2-methyl-N-phenylmaleimide, 4-methyl-N-phenylmaleimide, 2-ethyl-N-phenylmaleimide, 4-ethyl-N-phenylmaleimide, 2,6-diethyl-N-phenylmaleimide, and the like, or a mixture of any two or more thereof.
Succinimides contemplated for use in the practice of the present invention as component (B) have the following structure: 
wherein:
each Qxe2x80x2 is independently a lower alkyl or fluorinated lower alkyl,
Rxe2x80x3 is
(1) saturated straight chain alkyl or branched chain alkyl, optionally containing optionally substituted aryl moieties as substituents on said alkyl chain or as part of the backbone of said alkyl chain, and wherein said alkyl species have up to 20 carbon atoms,
(2) aromatic groups having the structure: 
wherein each Ar is an optionally substituted nobornyl, a disubstituted or trisubstituted aromatic or heteroaromatic ring having in the range of 3 up to 10 carbon atoms, and Z is:
(i) saturated straight chain alkylene or branched chain alkylene, optionally containing saturated cyclic moieties as substituents on said alkylene chain or as part of the backbone of the alkylene chain, or
(ii) polyalkylene oxides having the structure:
xe2x80x94[(CRxe2x80x22)rxe2x80x94Oxe2x80x94]qxe2x80x94(CRxe2x80x22)sxe2x80x94
wherein each Rxe2x80x2 is independently as defined above, r falls in the range of 1 up to 10, s falls in the range of 1 up to 10, and q falls in the range of 1 up to 50,
(3) di- or tri-substituted aromatic moieties having the structure: 
wherein each Rxe2x80x2 is independently as defined above, t falls in the range of 2 up to 10, u falls in the range of 2 up to 10, and Ar is as defined above
(4) polyalkylene oxides having the structure:
xe2x80x94[(CRxe2x80x22)rxe2x80x94Oxe2x80x94]qxe2x80x94(CRxe2x80x22)s
wherein each Rxe2x80x2 is independently as defined above, and wherein each of r, s and q are as defined above,
(5) a polycyclic olefinyl, or
(6) mixtures of any two or more thereof, and
each x is independently 0, 1 or 2, and
mxe2x89xa70.
Free-radical curing co-monomers contemplated for use in the practice of the present invention include electron poor olefins such as, for example, unsaturated anhydrides, (meth)acrylates, styrenes, cyanate esters, vinyl esters, divinyl compounds, and the like.
In preferred embodiments, anhydrides contemplated for use in the practice of the present invention include maleic anhydride, citraconic anhydride, itaconic anhydride, and the like, or Diels-Alder adducts of maleic anhydride, citraconic anhydride, itaconic anhydride, and the like, and cyclopentadiene. Diels-Alder adducts contemplated for use in the practice of the present invention have the following structure: 
wherein each Q is independently an alkyl or substituted alkyl, each x is independently 0, 1 or 2, and mxe2x89xa69.
Divinyl compounds contemplated for use in the practice of the present invention are present such that there is no greater than one equivalent of divinyl compound plus said polycyclic olefin per equivalent of bismaleimide. The divinyl compounds have the following structure:
CHRaxe2x95x90CRaxe2x80x94Q0.1xe2x80x94Yxe2x80x94Q0.1xe2x80x94CRaxe2x95x90CHRa
wherein:
each Ra is independently hydrogen, lower alkyl or aryl,
each Q is independently xe2x80x94Oxe2x80x94,xe2x80x94Oxe2x80x94C(O)xe2x80x94,xe2x80x94C(O)xe2x80x94 orxe2x80x94C(O)Oxe2x80x94,
xe2x80x94Yxe2x80x94 is:
(1) saturated straight chain alkylene or branched chain alkylene, optionally containing saturated cyclic moieties as substituents on said alkylene chain or as part of the backbone of the alkylene chain, wherein said alkylene species have at least 6 carbon atoms,
(2) di- or tri-substituted aromatic moieties having the structure: 
wherein each R is independently as defined above, Ar is as defined above, and each of t and u are as defined above,
(3) polyalkylene oxides having the structure:
xe2x80x94[(CR2)rxe2x80x94Oxe2x80x94]qxe2x80x94(CR2)sxe2x80x94
wherein each R is independently as defined above, and wherein each of r, s and q are as defined above,
(4) is derived from a dimer amine, and includes xe2x80x94(CH2)9xe2x80x94CH(C8H17)xe2x80x94CH(C8H17)xe2x80x94(CH2)9xe2x80x94,
(5) a siloxane, or
(6) mixtures of any two or more thereof.
Curing catalysts contemplated for use in the practice of the present invention include free-radical initiators such as peroxy esters, peroxy carbonates, hydroperoxides, alkylperoxides, arylperoxides, azo compounds, and the like.
The incorporation of polycyclic olefin monomers into a free radical curing thermoset imparts many useful properties to the final crosslinked material. It has been observed that these monomers increase the glass transition temperature of the thermoset while decreasing the coefficient of thermal expansion. Additionally, thermosets which contain polycyclic olefins have increased toughness versus those without these monomers. A further desirable benefit which can be attributed to these monomers when incorporated into a thermoset is low shrinkage upon cure. All of these properties are important in a variety of end use applications, such as for example optical disks, barrier films, medical appliances, and the like. In particular, the properties provided by these monomers are especially useful in semiconductor packaging applications such as, for example, die-attach adhesives. Invention compositions may be readily incorporated into die-attach formulations containing further components such as, for example, conductive fillers, to provide hydrophobic, low-shrinkage die-attach pastes.
Polycyclic olefin monomers contemplated for use in the practice of the present invention contain at least one unit of bicycloheptenyl unsaturation and are readily synthesized via Diels-Alder chemistry, as shown below in Scheme 1. 
The temperatures required for this reaction to proceed are generally between 150 and 250xc2x0 C. It is necessary to use an autoclave to conduct this reaction since all of the reactants have boiling points well below 100xc2x0 C. Cyclopentadiene need not be used directly since this component of the reaction can be readily generated in situ from the retro Diels-Alder reaction of dicyclopentadiene. Both norbornene and norbornadiene are commercially available and convenient to use. Alternatively, these materials could also be generated in situ from ethylene or acetylene and cyclopentadiene, respectively, as shown in Scheme 2. 
Rb=H, Me, higher alkyl, Ar, CN
As shown above, functionalized polycyclic olefin monomers are readily obtained via Diels-Alder chemistry. Further examples of functionalized polycyclic olefin monomers are shown below in Scheme 3. The reaction between cyclopentadiene and strong dienophiles such as, for example, maleic anhydride and N-alkyl maleimides, produces polycyclic olefin monomers which can increase adhesion of the thermoset material to a variety of surfaces. 
The polycyclic olefin monomers described in Schemes 1-3 are all high molecular weight analogs of norbornene or norbornadiene. As such, their vapor pressure is extremely low, resulting in very little outgassing or weight loss during high temperature cure. It is of note that these high molecular weight species are sufficiently reactive with electron deficient monomers to produce highly crosslinked networks. Indeed, electron rich polycyclic olefins readily copolymerize free radically with a variety of electron poor olefins, to give alternating copolymers, as shown in Scheme 4. 
Thus, the polycyclic olefin monomers contemplated for use in the practice of the present invention can be copolymerized with a variety of electron deficient monomers to give a thermosetting composition which is sufficiently reactive to provide a highly crosslinked network. This reactivity can be extended to a variety of functionalized electron deficient olefins, resulting in thermoset resins with a wide range of attractive properties.
Invention compounds are particularly useful in the microelectronics industry, where properties such as hydrophobicity, ionic purity, low shrinkage upon cure, and the like, are extremely important. Indeed, formulations comprising invention compounds are attractive candidates for a variety of electronic packaging applications, such as, for example, die-attach pastes. The use of invention compounds in die-attach formulations provides die-attach pastes with high glass transition temperatures. This feature is particularly important since state of the art microprocessors generate more heat during operation than previous generations of microprocessors.
The properties provided by invention compounds are also desirable in other microelectronic packaging applications, such as, for example, underfill, encapsulants, solder mask, and the like.